Conventionally, there is known a vehicle lamp unit which is provided with: a projection lens including a plurality of lenses disposed on an optical axis extending in a vehicle longitudinal direction; and a light source disposed at a rear side more significantly than a rear side focus surface of the projection lens and radiating a rear side finish surface of the projection lens, and which is characterized in that the rear side focus surface of the projection lens and the rear side finish surface of the projection lens are substantially coincident with each other, and on the rear side finish surface of the projection lens, a certain process of dispersing the light that is radiated by the light source is applied (refer to Patent Literature 1).
In addition, in Patent Literature 1, the following descriptive matters are set forth. That is, by employing the configuration as described above, in place of projecting an image of the light source which has been disposed in the vicinity of a rear side focal point of the projection lens (or an optical image formed in the vicinity of the rear side focal point of the projection lens by reflection light source from a reflection surface), an illuminance distribution is formed to have been uniformed on the rear side finish surface of the projection lens by way of action of the rear side finish surface of the projection lens that have been substantially coincident with the rear side focus surface of the projection lens (a fine, irregular shape exerted by emboss processing or the like applied to the rear side finish surface of the projection lens, for example). The thus uniformed illuminance distribution is enlarged and inverted and then projected forward via the projection lens; and therefore, it is possible to form predetermined light distribution patterns of the uniformed luminance distribution on a virtual vertical screen (which is disposed by about 25 m forward from a vehicle front surface, for example).
In addition, in Patent Literature 1, it is described that it is possible to restrain a color fringe exerted by color aberration, in comparison with a case in which a projection lens is composed of a single lens.